Explanatory factors for the observed effects of meditation and their particular importance in behaviour therapy research include the following 3 categories:

Category 1. Factors which are common to all strategies such as social support or therapeutic contact. Many clinical researchers have observed that controls with high face validity seem more likely to generate effects of similar magnitude to the intervention. Expectancy alone has also been shown in a number of studies positively to influence the apparent effect of meditation. An important factor which relates to the plausibility of the control interventions is the participant’s expectation that they will experience a benefit (or detriment)45. Despite this, only 24 studies took specific steps to gauge either the participants’ expectation of benefit or the perceived credibility of the various interventions.

Category 2. The possibility that strategies that draw volunteers from the community without using a predetermined threshold of dysfunction end up recruiting samples containing significant proportions of participants with sub-clinical scores. These “worried well”46 have little scope to improve, exerting a ceiling effect on the chosen measures and thus dilute any apparent effect of the intervention. In other words, behaviour therapy trials, especially trials that recruit from the general community, and even more especially those community-recruited trials seeking to demonstrate behavioural changes in normal participants (i.e. those with no diagnosed psychopathology) are fundamentally prone to type 2 errors in study design47. Since meditation was developed as a practice for everyday use by normal people rather than those with psychopathology, researchers have frequently recruited from the community. This issue is therefore of particular relevance to the work presented in this thesis.

Category 3. Other factors include regression to the mean. This is a phenomenon that most commonly occurs in studies in which participants are selected because they have extreme values on a certain variable, such as in clinical trials for which specific eligibility criteria are set. In this case, the participants will manifest an improvement simply because of the natural tendency for variables to approach the population mean over time, regardless of any effect (or lack thereof) from the intervention being studied48,and poor choice of outcome measures which are not specific and sensitive enough to detect change.

Dr Ramesh Manocha

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Sample size is obviously a key factor in determining the validity and generality of trial outcomes. It needs to be determined carefully to ensure that the research time, effort and support costs invested in any clinical trial are not wasted. Ideally, clinical trials should be large enough to detect reliably the smallest possible differences in the primary outcome with treatment that are considered clinically worthwhile. My review found that it was common for studies to be “underpowered”, failing to detect even large treatment effects because of inadequate sample size suggesting that resources may have been wasted for want of a slightly larger sample. Some ethics committees may object to recruiting patients into a study that does not have a large enough sample size for the trial to deliver meaningful information. Despite the importance of appropriate sample size, only 12 studies reported the use of a sample size calculation.
It is a widely accepted rule of thumb that trials with 30 or less participants per treatment arm are unsuited to conventional statistical analysis. In fact trials with less than 15 participants per treatment arm, while useful for generating hypotheses for further research, are not at all reliable for making conclusive statements. In my review, 78 studies used 30 participants or less per treatment arm . In fact 17 studies used 10 or less participants per treatment arm, making any kind of analysis futile (although this did not stop the investigators from conducting statistical analyses), whereas only 42 studies used more than 30 participants per treatment arm.

Dr Ramesh Manocha

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The Jadad scoring system is a widely used method of rating RCTs for basic methodological rigour. However it seems to be inadequately structured to meaningfully discern the methodological standard of meditation trials. For instance, while all trials might be randomised, only a minority described randomisation methods and few use the term “double blind”.

The blinding process in meditation trials is complex since it involves blinding of participants, raters, instructors, statisticians and other investigators.

It also demands that the comparator intervention is properly able to control for non-specific effects. Many trials feature some of these steps and others actually feature them all. And yet the Jadad score only applies one point for this crucial but complex and multifaceted factor. Similarly, very few trials described drop-outs.

The Jadad score of the studies in my review mostly ranged between 0 and 2. Trials with high scores did not seem to be much better designed than trials with lower scores. Thus the Jadad system does not usefully differentiate between trials with a methodology of a sufficient standard to discern effects specific to meditation, and those that do not have such a methodology. Despite evaluating other methodological rating systems none were appropriately orientated to be useful in discerning meditation research.

Dr Ramesh Manocha

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A head-to-head comparison is where two different approaches to meditation are compared. They are easier to conduct then sham meditation comparisons since elaborate deception strategies are not required, they have inherent authenticity and ethical problems are much less likely. Head-to-head trials are important and valuable because they allow comparison of different definitions, paradigms and approaches to meditation. They are especially useful given that there is no consensus even on what exactly meditation is. A disadvantage of such comparisons is that they may not necessarily allow for a clear distinction between meditation-specific and non-specific effects.

a head-to-head comparison where two different approaches to meditation are compared. They are easier to conduct since elaborate deception strategies are not required, have inherent authenticity and ethical problems are much less likely. Head-to-head trials are important and valuable in the current context because they allow comparison of different definitions, paradigms and approaches to meditation. They are especially useful given that there is no consensus even on what exactly meditation is. A disadvantage of such comparisons is that they may not necessarily allow for a clear distinction between meditation-specific and non-specific effects.
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There are a large number of reviews on the topic of meditation in the peer reviewed journal literature. Their conclusions are remarkably diverse, ranging from overwhelmingly positive to considerably negative. These disparities are explainable by factors such as the methodological standards set by the reviewers, whether or not the researchers were interested in differentiating between specific and non-specific effects and the researcher’s own affiliations. Generally speaking, the more rigorous the standards set by the reviewers, the less likely they were to express enthusiasm for meditation.

For more detail on how the meditation research can be sorted and analysed, check Dr Ramesh Manocha’s blog.

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Meditation research to date has been plagued by conceptual and methodological problems. One of the most significant difficulties involves developing control strategies involving interventions which blinded participants might consider plausible, that have no specific therapeutic effects. Randomisation and management of other sources of bias is another area of concern; a large number of controlled trials have used non-randomised, dissimilar cohorts.

Dr Ramesh Manocha further discusses the specific problems of defining meditation at his blog.

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It is difficult to make conclusions about meditation when the definition of the independent variable itself varies from study to study, if not from person to person. A homogeneous definition of meditation is essential for further progress in this field and yet, after almost 40 years of research the scientific community is unable to provide a truly consensus definition. Some argue that this is because meditation is actually a broad collection of disparate methods however it might be equally argued that the lack of consistent definition is symptomatic of our poor understanding.

More discussion on the definition of meditation can be found at Dr Ramesh Manocha’s blog.

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The Western scientific and health community of scientists and clinicians has generated in excess of 3,000 peer-reviewed articles on or referring to meditation (as featured in the major bibliographic databases such as MEDLINE and PsycINFO). However, despite this impressive accumulation of publications, the number of randomised controlled trials of meditation published per year—studies that would be regarded as serious explorations of meditation’s effects— reveal a different story. Although meditation is often a topic of superficial discussion amongst scientists and clinicians, it is rarely the subject of in-depth scientific examination.

More discussion on the quantity of scientific research exploring meditation can be found at Dr Ramesh Manocha’s blog.

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Researching meditation poses a unique challenge, since participants receiving the “inert” (or “placebo”) treatment must be involved in a placebo-like activity that nevertheless requires their active, conscious and conscientious involvement. They must also be sufficiently convinced of its authenticity to motivate them to participate at a level necessary to maintain the validity of the study.

More information about placebos can be found at Dr Manocha’s blog.

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Shapiro (1992) observed the effects of vipassana meditation on a small group of meditators and found that while most participants experienced positive results, a small number of meditators experienced distinctly negative states.

Glueck (1984) studied 110 participants and reported that the practice of transcendental meditation (TM) appeared to release repressed subconscious impressions. A small proportion of participants reacted adversely to this experience. Heide (1983, 1984) found that 54% of anxiety prone participants demonstrated increased anxiety during mantra meditation modelled on TM. Otis (1974) observed a cohort of 62 novices who tried TM and concluded that it was not suitable for those with serious emotional problems.

Read more about the research into the adverse effects of meditation here.

Ramesh Manocha.

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